Physiologus: On the Natures of Twelve Animals

...a naked man. It flees from him entirely original: "omnino", but when it sees a man clothed in garments, it attacks him and strives as much as it can to kill him. The fourth nature of the serpent is that when it is struck or fears being killed, it then guards its head more than its whole body. Whence, for greater defense, it forms a shield out of its entire body. And it places its head in the middle, thus exposing its whole body so that it might save only the head; for as long as its head remains unharmed, it can live, because its life is in its head.

From the sacred fountain meaning the baptismal font, you who were once renewed,
Do you sin again? Then you were a filicernus filicernus: an obscure Latin term for one bent with age or a participant in a funeral feast; here used to describe someone spiritually dead despite baptism.
Ever, therefore, be an imitator of the snake in these things as you grow old.
Let food be sparse so that your limbs are diminished referring to the practice of fasting to weaken the "fleshly" impulses,
Whence, when you eat, you shall help the poor.
Penitent, weep; also say often to the Lord: "Have mercy."
The opening of the stone signifies this path,
And the rock signifies Christ original: "xpm" (abbreviation for Christum); for indeed through Him,
Everyone is made new and receives a life that lacks an end.
By coming to His lofty temple,
So that you may drink the sacred and blessed Word,
Vomit out first the harmful poison you have in your heart.
In the heart, angers are more harmful than a snake,
And like mothers, they give birth to hatred.
In the heart are quarrels—no friends to goodness—and envies;
With proud furies conceived in the heart,
You despise your equals and those above you; with poisons
Such as these and many others, hearts are full.
In the heart, deceit and greed remain everywhere.
Being truly pure of these things, as if naked of clothing,
You shall put the demons to flight like the symbolic snake original: "angue tipicus",
As the sun's path drives back the blind shadows of night.